2015-09-25_REVISION - M1980183 (3)

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Mr. Tyler O'Donnell RE: Datum Shift Page 2 of 2 In 1929 the NGVD (National Geodetic Vertical Datum ) 29 was established. This was the vertical control datum in the country until it was replaced by NAVD 88, which is still in use today. The topographic map in use in 1980, when the water level contour map was made and included in the original Brannan Pit 29 application, was dated 1965 (photo revised 1979). That map was revised in 1994. Therefore the 1965 map was the one in use in 1980. A copy of the legends of both maps is attached. The vertical datum in use in 1980 was NGVD29. NOAA has an online tool called VERTCON: http://www.ngs.noaa.gov/cgi-bin/VERTCON/vert con.prl This tool converts NGVD 29 to NAVD88. Using a NGVD29 datum (1965 map) of 5005 feet, the tool result is a NAVD88 datum of 5007.878 ft. Attached is the print of the result. Based on this conversion, our drain elevation of 5007' at the west end is accurate and would replicate the historic ground water level. Datum conversion using the VERTCON tool is appropriate for the purposes of correlating this groundwater data. Attached is a revised Exhibit E adding a NAVD88 datum note. Conclusion The french drain specified in AM -02 is designed to permanently eliminate groundwater mounding on the south and west sides of Pit 29. By placing the french drain at the elevation and gradient of the pre -mining groundwater surface elevation, the plan is designed to prevent future groundwater levels from exceeding those pre -mining contours. If you have any questions please call me at your convenience. Cordially, Applegate Group, Inc. Tom Hatton Senior Project Manager TH/ta Enclosures cc: Eugene Riordan, Esq. Alex Schatz, Brannan Sand and Gravel AG File No. 10-116 NA101 16 Brannan Pit 29\Disciplines (Technical)\WRPM\Water Rights\Amendment 2.2\1)atum letter to tyler.docx